The present invention relates to a tip for a cutting tool which cuts and planes a surface of a piece such as a race surface of a bearing which is in a rolling contact with rolling elements.
Generally, a member which has a surface which is in a rolling contact with rolling elements is treated with heat for the purpose of extending the life-time of the member against rolling fatigue. Such heat treatment is applied to the whole member or only to its surface which is brought into a rolling contact with the rolling elements. After such heat treatment, the surface to be in contact with the rolling elements is cut away so that residual stress in compression is applied to the cut portion, for the purpose of further extending the life-time of the member against rolling fatigue. The presence of the residual stress in compression especially in the vicinity of the surface is very effective in extending the life.
A tip of a conventional type for a cutting tool is shown in FIG. 4. The tip has a rake surface S of an angle of negative value .theta.1 at a cutting portion thereof. That is, the rake surface S has a negative slope with respect to a cutting direction of the tip as shown by an arrow. A corner defined by the rake surface S and a front flank F is rounded.
The above prior art tip, however, cannot apply sufficient amount of residual stress of compression to the vicinity of the surface of a piece or material to be cut, because of the shape as described above, and what is worse, the residual stress present at the surface is apt to be of tension. The residual stress in tension affects the life-time of the material against rolling fatigue. Therefore, in that case, the portion where the residual stress in tension is present must be abraded to be removed. In other words, with the prior art tip, stress of compression sufficient to extend the life-time of the material against the rolling fatigue cannot be applied.